Piston of piston type fluid pump motor

ABSTRACT

A piston used in a piston type fluid pump motor comprises a plurality of piston heads which are each rotatably mounted on a single rod by ball-and-socket joints. Reduced friction between the piston heads and a cylinder wall avoids seizure of the piston and cylinder wall during operation.

tlnitd States Patent Miyao et al. 1 Feb. 18, 1975 [54] PISTON 0F PISTONTYPE FLUID PUMP 2,956,845 10/1960 Wahlmark 92/256 MOTOR 3,382,813 5/1968Schauer 91/506 [75] Inventors: Takayaki Miyao; Hiroaki Maeda,

both of Toyota; Masanori Sato, Nagoya, all of Japan [73] Assignee: AisinSeiki C0,, Ltd., Kariya-shi,

Aichi-ken, Japan [22] Filed: .Ian. 16, 1973 [2]] Appl. No.: 324,128

[30] Foreign Application Priority Data Feb. 18, 1972 Japan 47-17330 Jan.27, 1972 Japan 47-10106 [52] 11.8. C1. 91/488 [51] Int. Cl. ..F01b 13/04[58] Field of Search 91/499507; 92/256 [56] References Cited UNITEDSTATES PATENTS 893,558 7 9 Williams 91/507 FOREIGN PATENTS ORAPPLICATIONS 699,027 12/1964 Canada 91/ 199 1,023,811 2/1963 GreatBritain 220,417 8/1924 Great Britain 1, 91/505 Primary Examiner-WilliamL. Freeh Attorney, Agent, or FirmOblon, Fisher, Spivak, McClelland &Maier 13 Claims, 17 Drawing Figures PATENTEU F531 8 I975 SHEET 2 OF 7SHEET 3 or 7 MENTED FEB] 81975 PATENTEU 71.866519 SHEET 8 OF 7 FIG.||

PISTON OF PISTON TYPE FLUID PUMP MOTOR BACKGROUND OF THE INVENTION 1.Field Of The Invention This invention relates generally to a piston usedin a piston type fluid pump motor and more particularly to a uniquepiston having reduced friction between piston heads and a cylinder wall.

2. Disclosure Of the Prior Art In the past, various types of fluid pumpmotors have been proposed. While somewhat satisfactory, prior fluid pumpmotors have had the disadvantages that friction associated with a pistonhead caused seizure of the piston head with a cylinder wall requiringdown time and repair or replacement.

SUMMARY OF THE INVENTION Accordingly, one object of the presentinvention is to provide a new and improved unique piston.

Another object of the present invention is to provide a new and improvedunique piston of a piston type fluid pump motor for minimizing frictionbetween the piston and the wall of a cylinder so as to prevent aseizure.

Briefly, in accordance with this invention, the foregoing and otherobjects are in one aspect attained by utilizing a piston in a pistontype fluid pump motor which comprises a plurality of piston heads whichare each rotatably mounted on one rod by ball-and-socket joints.

BRIEF DESCRIPTION OF THE DRAWINGS Various other objects, features andadvantages of the invention will be more fully appreciated as the samebecomes better understood from the following detailed description whenconsidered in connection with the accompanying drawings, wherein likereference characters designate like or corresponding parts throughoutthe several views, and in which:

FIG. 1 is a front view of one embodiment of a piston according to thisinvention;

FIG. 2 is a sectional view taken along the line II-II of FIG. 1;

FIG. 3 is a sectional view taken along the line III-III of FIG. 2;

FIG. 4 is a sectional view taken along the line IVIV of FIG. 2;

FIG. 5 is a sectional view of one embodiment of an axial piston typehydraulic pump motor having a piston according to this invention;

FIG. 6 is a partial enlarged sectional view of FIG. 5;

FIG. 7 is a front view of another embodiment of a piston according tothis invention;

FIG. 8 is a sectional view taken along the line VIII- -VIII in FIG. 7;

FIG. 9 is a sectional view taken along the line IX-IX in FIG. 8;

FIG. 10 is a sectional view taken along the line X-X in FIG. 8;

FIG. 11 is a front view of yet another embodiment of a piston accordingto this invention;

FIG. 12 is a sectional view taken along the line XII- -XII in FIG. 11;

FIG. 13 is a sectional view taken along the line XIII- -XIII in FIG. 12;

FIG. 14 is a sectional view taken along the line XIV--XIV in FIG. 12;and,

FIG. 15 is a sectional view of an embodiment of the invention used in anaxial piston type fluid pump motor.

FIG. 16 is a front view of the embodiment of a piston according to thisinvention shown in FIG. 15; and,

FIG. 17 is a sectional view taken along the line XV-XV in FIG. 16.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to thedrawings, wherein like reference characters designate identical, orcorresponding parts throughout the several views, and more particularlyto FIG. I a piston 10 comprises two piston heads 12 and 14 and a rod 16.

The piston head 12, as shown in FIGS. 2 and 3, in sectional views,comprises a housing 18 of a substantially cylindrical shape and a pairof bushes 24 and 26 of a semicylindrical shape which are respectivelyfitted in the housing and fixed to the housing by bending both ends 20and 22 of the housing in a radial direction. As shown in FIGS. 2 and 4,the piston head 14 comprises a housing 28 of a substantially cylindricalshape and a pair of bushes 34 and 36 of a semicylindrical shape whichare respectively fitted in the housing and fixed thereto by bending oneend 30 and the housing in a radial direction and a fitting ring 32within the housing. The piston head 12 is rotatably mounted or jointedat substantially a middle part of the rod 16 by a ball-andsocket jointwhich is formed with a convex spherical surface 38 formed at asubstantially middle part of the rod 16 and a concave spherical surface40 and 42 formed in the bushes 24 and 26 and positioned facing theconvex spherical surface. The piston head 14 is also rotatably jointedat one end of the rod 16 by a ball-andsocket joint which is formed witha convex spherical surface 44 formed at one end of the rod 16 and aconcave spherical surface 46 and 48 formed in the bushes 34 and 36 andpositioned facing the convex spherical surface.

As seen in FIG. 2, two grooves 50 and 52 are formed on the outer surfaceof the piston head 14 for lubricating the outer surface and the cylinderwall. A groove 54 is formed on the outer surface of the piston head 12for supplying a lubricant between the outer surface and the cylinderwall. The groove 54 is connected, through a hole 58 formed in the pistonhead 12 and the rod 16, to a hole 56 formed in the rod 16.

In FIGS. 5 and 6, the reference numeral 60 designates an axial pistontype hydraulic pump motor which is a piston type fluid pump motor. Aplurality of cylinders 68 are formed in an axial direction in a cylinderbarrel 66 connected to a rotary shaft 62 with a plurality of pins 64treated by crowning. Within the cylinders 68, each piston 10 isrespectively slidably fitted. The other end of the rod 16 of the piston10 is jointed through a ball-and-socket joint to a shoe 74 slidablymounted on a sliding surface 72 of a swash plate 70. The ball-andsocketjoint is formed with a convex spherical surface 76 formed on the otherend of the rod 16 and a concave spherical surface 78 formed in the shoe74 facing the convex spherical surface.

When the rotary shaft 62 is rotated by suitable means and a lubricant atlow pressure is supplied through the oil-passage 80, the cylinder barrel66 is also rotated by the rotation of the rotary shaft 62, so that thepiston 10 is reciprocated in the cylinder 68 by the slant of the slidingsurface 72 of the swash plate 70. Accordingly, the lubricant at lowpressure supplied through the oilpassage 80 of the slot for lowpressure, is exhausted as a lubricant at high pressure from theoil-passage 82 of the slot for high pressure.

It has been well-known that a motor can perform a reversal operation. Inthat case, the piston is pressed to the slant plate 70 by the hydraulicpressure, whereby a force W is applied to the other end of the rod 16 ofthe piston 10 by the slant of the sliding surface 72 of the swash plate70 as shown in FIG. 6.

When a conventional piston formed with a single part is used, a gap forsliding is provided between the outer surface of the piston and thecylinder wall, so that an axis of the piston is inclined to an axis ofthe cylinder whereby the piston contacts the cylinder wall at both endsof the outer surface facing it.

The contact between the piston and the cylinder wall is substantiallylinear so that the pressure at the contact part is high enough to causethe lubricant membrane to break in addition to causing friction betweenthe piston and cylinder wall and seizure of the piston and cylinder.

On the other hand, when the piston 10 of this invention is employed, thepiston heads 12 and 14 are respectively jointed to the rod 16 by theball-and-socket joint so as to be rotatable. The axis of the rod 16 isinclined to the axis of the cylinder 68, however, the axes of the pistonheads 12 and 14 are not respectively inclined to the axis of thecylinder 68 even though the piston head axes are not consistent as seenin FIG. 6 so that the piston heads 12 and 14 are respectively in surfacecontact with the cylinder wall, so that there is virtually no frictionbetween the piston heads and the cylinder wall, and accordingly noseizure of the piston heads and the cylinder wall occurs.

Incidentally, in the drawings, each piston head is jointedlongitudinally through the ball-and-socket joint at the middle portionof the rod 16. However, it should be understood that it is not alwaysnecessary to joint the piston heads at the middle portions of the rod.If the piston heads are jointed to the middle part of the rod, uniformpressure at the contact surface between the outer surface of the pistonhead and the cylinder wall is advantageously provided. It should befurther understood that when the piston of this invention is used, theball-and-socket joint may be placed in the cylinder at any time.

In another embodiment of the present invention shown in FIGS. 7-10, thepiston 84 comprises a pair of piston heads 86 and 88 and a rod 90. Thepiston head 86 comprises a housing 92 of a substantially cylindricalshape and a bush 98 of a substantially cylindrical shape which is fittedwithin the housing and fixed to the housing by bending one end 94 of thehousing in a radial direction and providing a caulk 96.

The piston head 88 comprises a housing 100 of a substantiallycylindrical shape and a bush 106 of a substantially cylindrical shapewhich is fitted within the housing and fixed to the housing by bendingone end 102 of the housing in a radial direction and providing a caulk104. The piston head 86 is rotatably jointed to a middle portion of therod 90 by a ball-and-socket joint formed with a convex spherical surface108 formed at a middle portion of the rod 90 and a concave sphericalsurface 110 formed by a bush 98 to face surface 108.

The piston head 88 is also rotatably jointed to one end of the rod 90 bya ball-and-socket joint formed with the convex spherical surface 112formed at one end of the rod and a concave spherical surface 114 formedin the bush 106 to face surface 112. A part of the concave sphericalsurface is formed by caulking one end 116 of the bush 98.

A similar operation and result of the piston of a first embodiment isattained by the piston 84 of an alternative embodiment of thisinvention.

In the alternative embodiment shown in FIGS. 11-14, a piston 120comprises a pair of piston heads 122 and 124 and a rod 126. The pistonhead 122 is formed by a single part of a cylindrical shape, and isrotatably jointed to a middle portion of the rod 126 by aball-and-socket joint having a convex spherical surface 128 formed at amiddle portion of the rod 126 and a corresponding concave sphericalsurface 130 formed in the piston head. The piston head 124 similarly isformed by a single part of a cylindrical shape and is rotatably jointedto one end of the rod 126 by a ball-andsocket joint having a convexspherical surface 132 formed at one end of the rod 126 and acorresponding concave spherical surface 134 formed in the piston head.

A part of the concave spherical surface 130 is formed by caulking aportion 136 of the piston head 122, and a part of the concave sphericalsurface 134 is formed by caulking a portion 138 of the piston head 124.

A similar operation and result can be attained with this embodiment aswith the first embodiment. In the embodiments described above, twopiston heads are employed; however, it should be understood that morethan two piston heads can be employed.

As stated above, the piston of this invention comprises a plurality ofpiston heads which are each rotatably jointed to one rod byball-and-socket joints, so that there is virtually no friction betweenthe piston and the cylinder wall and accordingly no seizure of thepiston and the cylinder wall results.

In FIG. 15, the reference numeral 10 designates an axial piston typefluid pump motor wherein a casing 211 is formed by connecting threedivisional parts 212, 214 and 216 with a plurality of bolts 218. In acasing 211, a swash plate 220 placed at left side thereof is pivoted bythe casing 211 with a trunnion axis (which is perpendicular to thepaper), and a valve plate 222 is fixed to the casing 211 by a pluralityof pins 224. A rotary axis 230 connecting the swash plate 220 throughholes 226 and 228 to the valve plate 222, is pivoted by the casing 211through bearings 232 and 234.

On the rotary shaft 230, a cylinder barrel 236 is provided between theswash plate 220 and the valve 222. A cylinder barrel 236 is divided intotwo parts 238 and 240. One part 238 connected to the valve 222 isrotatably and axis-swingably jointed to a rotary shaft 230 by aplurality of keys treated by crowning and is pressed to the valve 222 bya spring 244. The other part is mounted to the rotary shaft 230. Thepistons 248 fitted to each of a plurality of cylinders 246 formed in thecylinder barrel 236 are each rotatably jointed to the rod 252 by auniversal joint wherein the first piston head 254 sliding in one part238 and a second piston head 256 sliding in the other part 240 arejointed to one rod 252 connected through a shoe 250 to the swash plate220.

In FIG. 15, the rotary center of the first piston head 254 to the rod252 of the piston 248 corresponds to the centroid of the piston head.The rotary center of the second piston head 256 corresponds to thecentroid of a piston-shoe system consisting of the piston 248 and theshoe 250. In the piston 248 shown in FIGS. 16 and 17, the second pistonhead 256 has four lubricant recesses 286 which are each connected to ahole 288 through holes 290 so as to provide static bearing pressure atthe movement. The second piston head 256 is rotatably jointed at asubstantially middle portion of a rod 252 by a ball-and-socket jointwhich is formed with a convex spherical surface 278 formed at thesubstantially middle portion of the rod 252, and a concave sphericalsurface 280 formed in a bush 272, which is fixed in a housing 266 by acaulking 270. A slot 294 for low pressure and a slot 296 for highpressure are formed on the valve 222. When the rotary shaft 230 isdriven by suitable power to supply a low pressure fluid from the slot294, the cylinder barrel 236 is rotated by the rotation of the rotaryshaft 230, so that each piston is reciprocated in the cylinder by theincline of the swash plate 220. The low pressure fluid supplied from theslot 294 is exhausted as a high pressure fluid from the slot 296 toprovide a pumping action.

It has been known that a motor action can be provided by a reversalaction. In a motor operation, a centrifugal force proportional to weightand square of rotary speed is provided to each of the pistons 248 andshoes 250. However, the other part 240 of the cylinder barrel 236 ismounted to the rotary shaft 230. Each piston 248 is rotatably jointed tothe rod 252 by a balland-socket joint through the first piston head 254sliding in one part of the cylinder barrel 236 and the second pistonhead 256 sliding in the other part, and the rotary center of the firstpiston head 254 to the rod 252 corresponds to the centroid of the pistonhead. Similarly, the rotary center of the second piston head 256 to therod 252 corresponds to the centroid of the piston-shoe system.Accordingly, a centrifugal force applied to the piston-shoe system isreceived by the rotary shaft 230 and does not reach one part 238. Thefriction force between the second piston head 256 and the cylinder wallis increased by the centrifugal force, but the friction force betweenthe first piston head 254 and the cylinder wall is not increased by thecentrifugal force. Accordingly, the disadvantages of decrease of volumeefficiency, friction and the seizure of the one part 238 and the valveplate 222 can be completely overcome by the centrifugal force in thepiston-shoe system. When the rotary shaft 230 is bent, the cylinder 246formed in the cylinder barrel 236 is curved but no trouble occursbecause the piston heads 254 and 256 are rotatably jointed to the rod252.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeunderstood that within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described herein.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

1. A piston used in a piston type fluid pump motor which comprises atleast two piston heads fitted in a cylinder barrel having coaxiallyaligned portions, each of said piston heads being rotatably jointed by aballand-socket joint to a rod which is movably connected to a swashplate,

whereby a torque generated on said swash plate is transmitted to saidcylinder through said piston heads.

2. A piston according to claim 1, wherein each of said piston headscomprises:

a housing of a substantially cylindrical shape rotatably jointed by saidball-and-socket joint formed with a convex spherical surface on said rodand a concave spherical surface on said piston head.

3. A piston according to claim 1, wherein the other end portion of saidrod is connected to a shoe which is slidably fitted onto a swash plate.

4. A piston according to claim 1, wherein a shoe is fitted to one end ofsaid rod and slidably fitted to a swash plate whereby said rod can movereciprocally.

5. A piston according to claim 1, wherein a bush is mounted in saidpiston head to joint with said rod by said ball-and-socket joint.

6. A piston according to claim 1, wherein said piston is used in anaxial piston type fluid pump motor.

7. A piston according to claim 1, which further comprises a lubricantrecess on each of said piston heads which is connected to a lubricantpassage in a rod.

8. A piston as set forth in claim 1, wherein said rod has a middleportion and two end] portions.

9. A piston according to claim 1, wherein one of said piston heads isjointed at the middle portion of the rod and a second of said pistonheads is jointed to one end portion of said rod.

10. A piston as set forth in claim 9, further comprisdrive means forapplying a torque to said piston heads; and

means for providing a reaction force to the other end portion of saidrod.

11. A piston according to claim 1, wherein one of said piston heads isfitted to one part of a cylinder barrel connected to a valve androtatably jointed to a rotary shaft, and the other of said piston headsis fitted to a separate part of said cylinder barrel mounted to saidrotary shaft.

12. A piston as set forth in claim 10, wherein said means for providinga reaction force to the other end portion of said rod is a swash plate.

13. A piston according to claim 11, wherein a rotary center of saidfirst piston head corresponds to a cen troid of said piston and a rotarycenter of said second piston head corresponds to a centroid of apiston-shoe system.

1. A piston used in a piston type fluid pump motor which comprises atleast two piston heads fitted in a cylinder barrel having coaxiallyaligned portions, each of said piston heads being rotatably jointed by aball-and-socket joint to a rod which is movably connected to a swashplate, whereby a torque generated on said swash plate is transmitted tosaid cylinder through said piston heads.
 2. A piston according to claim1, wherein each of said piston heads comprises: a housing of asubstantially cylindrical shape rotatably jointed by saidball-and-socket joint formed with a convex spherical surface on said rodand a concave spherical surface on said piston head.
 3. A pistonaccording to claim 1, wherein the other end portion of said rod isconnected to a shoe which is slidably fitted onto a swash plate.
 4. Apiston according to claim 1, wherein a shoe is fitted to one end of saidrod and slidably fitted to a swash plate whereby said rod can movereciprocally.
 5. A piston according to claim 1, wherein a bush ismounted in said piston head to joint with said rod by saidball-and-socket joint.
 6. A piston according to claim 1, wherein saidpiston is used in an axial piston type fluid pump motor.
 7. A pistonaccording to claim 1, which further comprises a lubricant recess on eachof said piston heads which is connected to a lubricant passage in a rod.8. A piston as set forth in claim 1, wherein said rod has a middleportion and two end portions.
 9. A piston according to claim 1, whereinone of said piston heads is jointed at the middle portion of the rod anda second of said piston heads is jointed to one end portion of said rod.10. A piston as set forth in claim 9, further comprising: drive meansfor applying a torque to said piston heads; and means for providing areaction force to the other end portion of said rod.
 11. A pistonaccording to claim 1, wherein one of said piston heads is fitted to onepart of a cylinder barrel connected to a valve and rotatably jointed toa rotary shaft, and the other of said piston heads is fitted to aseparate part of said cylinder barrel mounted to said rotary shaft. 12.A piston as set forth in claim 10, wherein said means for providing areaction force to the other end portion of said rod is a swash plate.13. A piston according to claim 11, wherein a rotary center of saidfirst piston head corresponds to a centroid of said piston and a rotarycenter of said second piston head corresponds to a centroid of apiston-shoe system.